EXPERIMENTAL FISH EMBRYOLOGY 



hl3 



Stippled daughters Stal 



Stat Sl.'ppled sons 



it Cold Bonf) and 



daughters 

 ■ I Cold platyfish — 



5l8t 



Stippled sons 

 and daughters 

 3 Stippled platyfishes - 



StSt Stippled sons 

 and daughters 



This diagram Illustrates the way In which the gray or stipple pattern of the platy- 

 fish is inherited. In the pair on the left, the father carries the dominant factor (StSt) 

 for stippling while the mother is non-stippled (stst) . The parents are designated as P-,. 

 The first filial generation (Fj) , obtained from this mating, are all stippled (Stst) like 

 their father. Similar results are obtained when the mother (see pair on right) is the 

 stippled parent (StSt) and the father is non-stippled. The offspring of this mating are 

 also all stippled, this time like their mother (Stst). When the individuals of the first 

 generation (Fj) are bred> together from either series, and the second generation (Fo) is 

 produced, the following results are obtained: there are three stippled fishes (StSt) or 

 (Stst) to every non-stlppled one (stst) . There are male and female representatives in 

 each group. Tills is an example of simple mendelian inheritance of a single heritable 

 character. The stippling is actually due to the presence in the skin of very small black 

 cells, technically known as mlcromelanophores . 



w z 



Noll spoiled mother sp »\\ 



^^^-'■■M 



L Z 



Sp Sp spotted father 



^!g:>:i 



w z 



Spotted daughters sp Sp 





z z 



Sp sp Spoiled sons 



W 2 



Non spotted daughters sp sp 



w z 



spoiled dauehlcrs sp Sp 



Spotted fiona 



Spoiled sons 



This diagram Illustrates the peculiar way in which the spotted (Sp) pattern is in- 

 herited. The female Is represented by the formula W Z while the male is Z Z. The spotted 

 factor is associated with sex. Wlien the spotted platy is the male parent (Zsp Zsp) and a 

 non-spotted platy is the female parent (Wsp Zsp) , all the offspring of the mating, both 

 the sons and daughters, are spotted like their father. When the spotted individuals of 

 the first generation (Fj^) are mated together, brother to sister, t}ie ratio of three spot- 

 ted platyfishes to one non-spotted is obtained in the second generation (Fo) . Up to this 

 point the results of this mating resemble tlie inheritance of the stippling factor, but 

 note the following significant fact: all the non-spotted fishes obtained in the second 

 generation are females. And the spotted platyfishes contain both males and females, but 

 there are two spotted sons to every non-spotted daughter. This is an example of the In- 

 heritance of a sex-linked heritable factor. A similar type of Inheritance is found in 

 birds and moths for certain characters. 



